The instant invention provides novel processes and intermediates useful in the preparation of certain N-(indole-2-carbonyl)-xcex2-alaninamide compounds, which compounds are glycogen phosphorylase inhibitors useful in the treatment of diseases such as hypercholesterolemia, hyperglycemia, hyperinsulinemia, hyperlipidemia, hypertension, atherosclerosis, diabetes, diabetic cardiomyopathy, infection, tissue ischemia, myocardial ischemia, and in inhibiting tumor growth.
Despite the early discovery of insulin and its subsequent widespread use in the treatment of diabetes, and the later discovery of, and use of, sulfonylureas (e.g. Chlorpropamide(trademark) (Pfizer), Tolbutamide(trademark) (Upjohn), Acetohexamide(trademark) (E. I. Lilly), Tolazamide(trademark) (Upjohn), and biguanides (e.g. Phenformin(trademark) (Ciba Geigy), and Mefformin(trademark) (G. D. Searle)) as oral hypoglycemic agents, therapeutic regimens for the treatment of diabetes remain less than satisfactory. The use of insulin, necessary in about 10% of diabetic patients in which synthetic hypoglycemic agents are not effective (Type 1 diabetes, insulin dependent diabetes mellitus), requires multiple daily doses, usually by self-injection. Determination of the proper dosage of insulin requires frequent estimations of sugar levels in the urine or blood. The administration of an excess dose of insulin causes hypoglycemia, with effects ranging from mild abnormalities in blood glucose to coma, or even death. Treatment of non-insulin dependent diabetes mellitus (Type 2 diabetes) usually consists of a combination of diet, exercise, oral agents, e.g., sulfonylureas, and, in more severe cases, insulin. However, clinically available hypoglycemic agents can have other side effects that limit their use. In any event, where one of these agents may fail in an individual case, another may succeed. A continuing need for hypoglycemic agents, which may have fewer side effects or succeed where others fail, is clearly evident.
Atherosclerosis, a disease of the arteries, is recognized to be the leading cause of death in the United States and Western Europe. The pathological sequence leading to atherosclerotic development and occlusive heart disease is well known. The earliest stage in this sequence is the formation of xe2x80x9cfatty streaksxe2x80x9d in the carotid, coronary, and cerebral arteries, and in the aorta. These lesions are yellow in color due to the presence of lipid deposits found principally within smooth-muscle cells and in macrophages of the intima layer of the arteries and aorta. It is further postulated that most of the cholesterol found within the fatty streaks, in turn, gives rise to development of the so-called xe2x80x9cfibrous plaquexe2x80x9d, which consists of accumulated intimal smooth muscle cells laden with lipid and surrounded by extra-cellular lipid, collagen, elastin, and proteoglycans. These cells, plus matrix, form a fibrous cap that covers a deeper deposit of cell debris and more extra cellular lipid, which comprises primarily free and esterified cholesterol. The fibrous plaque forms slowly, and is likely in time to become calcified and necrotic, advancing to the so-called xe2x80x9ccomplicated lesionxe2x80x9d which accounts for the arterial occlusion and tendency toward mural thrombosis and arterial muscle spasm that characterize advanced atherosclerosis.
Epidemiological evidence has firmly established hyperlipidemia as a primary risk factor in causing cardiovascular disease (CVD) due to atherosclerosis. In recent years, medical professionals have placed renewed emphasis on lowering plasma cholesterol levels, and low density lipoprotein cholesterol in particular, as an essential step in prevention of CVD. The upper limits of so-called xe2x80x9cnormalxe2x80x9d cholesterol are now known to be significantly lower than heretofore appreciated. As a result, large segments of Western populations are now recognized to be at particular high risk. Such independent risk factors include glucose intolerance, left ventricular hypertrophy, hypertension, and being male. Cardiovascular disease is especially prevalent among diabetic subjects, at least in part because of the existence of multiple independent risk factors in this population. Successful treatment of hyperlipidemia in the general population, and in diabetic subjects in particular, is therefore of exceptional medical importance.
Hypertension (high blood pressure) is a condition that occurs in the human population as a secondary symptom to various other disorders such as renal artery stenosis, pheochromocytoma, or endocrine disorders. However, hypertension is also evidenced in many patients in whom the causative agent, or disorder, is unknown. While such essential hypertension is often associated with disorders such as obesity, diabetes, and hypertriglyceridemia, the relationship between these disorders has not been elucidated. Additionally, many patients present with symptoms of high blood pressure in the complete absence of any other signs of disease, or disorder.
It is known that hypertension can directly lead to heart failure, renal failure, and stroke, which conditions are all capable of causing short-term death. Hypertension also contributes to the development of atherosclerosis, and coronary disease, which conditions gradually weaken a patient and can lead, in long-term, to death.
The precise etiology of essential hypertension is unknown, although a number of factors are believed to contribute to the onset of the disease. Among such factors are stress, uncontrolled emotions, unregulated hormone release (the renin, angiotensin, aldosterone system), excessive salt and water due to kidney malfunction, wall thickening and hypertrophy of the vasculature resulting in vascular constriction, and genetic pre-disposition.
The treatment of essential hypertension has been undertaken bearing the foregoing factors in mind. Thus, a broad range of xcex2-blockers, vasoconstrictors, angiotensin converting enzyme (ACE) inhibitors, and the like have been developed and marketed as antihypertensive agents. The treatment of hypertension utilizing such agents has proven beneficial in the prevention of short-interval deaths such as heart failure, renal failure, and brain hemorrhaging (stroke). However, the development of atherosclerosis, or heart disease due to hypertension over a long period of time, remains a problem. This implies that, although high blood pressure is being reduced, the underlying cause of essential hypertension remains unresponsive to this treatment.
Hypertension has further been associated with elevated blood insulin levels, a condition known as hyperinsulinemia. Insulin, a peptide hormone whose primary actions are to promote glucose utilization, protein synthesis, and the formation and storage of neutral lipids, also acts, inter alia, to promote vascular cell growth and increase renal sodium retention. These latter functions can be accomplished without affecting glucose levels and are known causes of hypertension. Peripheral vasculature growth, for example, can cause constriction of peripheral capillaries; while sodium retention increases blood volume. Thus, the lowering of insulin levels in hyperinsulinemics can prevent abnormal vascular growth and renal sodium retention caused by high insulin levels and thereby alleviate hypertension.
Cardiac hypertrophy is a significant risk factor in the development of sudden death, myocardial infarction, and congestive heart failure. These cardiac events are due, at least in part, to increased susceptibility to myocardial injury after ischemia and reperfusion which can occur in both out-patient and perioperative settings. There is currently an unmet medical need to prevent or minimize adverse myocardial perioperative outcomes, particularly perioperative myocardial infarction. Both cardiac and non-cardiac surgery are associated with substantial risks for myocardial infarction or death, and some 7 million patients undergoing non-cardiac surgery are considered to be at risk, with incidences of perioperative death and serious cardiac complications as high as 20-25% in some instances. In addition, of the 400,000 patients undergoing coronary by-pass surgery annually, perioperative myocardial infarction is estimated to occur in 5% and death in 1-2%. There is currently no commercial drug therapy in this area which reduces damage to cardiac tissue from perioperative myocardial ischemia or enhances cardiac resistance to ischemic episodes. Such a therapy is anticipated to be life-saving and reduce hospitalizations, enhance quality of life and reduce overall health care costs of high risk patients. The mechanism(s) responsible for the myocardial injury observed after ischemia and reperfusion is not fully understood, however, it has been reported (M. F. Allard, et al. Am. J. Physiol., 267, H66-H74, (1994) that pre-ischemic glycogen reduction is associated with improved post-ischemic left ventricular functional recovery in hypertrophied rat hearts.
Hepatic glucose production is an important target for Type 2 diabetes therapy. The liver is the major regulator of plasma glucose levels in the post absorptive (fasted) state, and the rate of hepatic glucose production in Type 2 diabetes patients is significantly elevated relative to normal individuals. Likewise, in the postprandial (fed) state, where the liver has a proportionately smaller role in the total plasma glucose supply, hepatic glucose production is abnormally high in Type 2 diabetes patients.
Glycogenolysis is an important target for interruption of hepatic glucose production. The liver produces glucose by glycogenolysis (breakdown of the glucose polymer glycogen) and gluconeogenesis (synthesis of glucose from 2- and 3-carbon precursors). Several lines of evidence indicate that glycogenolysis may make an important contribution to hepatic glucose output in Type 2 diabetes. First, in normal post absorptive man, up to 75% of hepatic glucose production is estimated to result from glycogenolysis. Second, patients having liver glycogen storage diseases, including Hers"" disease (glycogen phosphorylase deficiency), display episodic hypoglycemia. These observations suggest that glycogenolysis may be a significant process for hepatic glucose production.
Glycogenolysis is catalyzed in liver, muscle, and brain by tissue-specific isoforms of the enzyme glycogen phosphorylase. This enzyme cleaves the glycogen macromolecule releasing glucose-1-phosphate and a new shortened glycogen macromolecule. Two types of glycogen phosphorylase inhibitors have been reported to date: glucose and glucose analogs [J. L. Martin, et al., Biochemistry, 30, 10101, (1991)], and caffeine and other purine analogs [P. J. Kasvinsky, et al., J. Biol. Chem., 253, 3343-3351 and 9102-9106 (1978)]. These compounds, and glycogen phosphorylase inhibitors in general, have been postulated to be of potential use for the treatment of Type 2 diabetes by decreasing hepatic glucose production and lowering glycemia. See, for example, T. B. Blundell, et al., Diabetologia, 35 (Suppl. 2), 569-576 (1992), and Martin et al., supra.
Recently, glycogen phosphorylase inhibitors have been disclosed in, inter alia, PCT International Application Publication No. WO 97/31901, and in commonly-assigned U.S. Pat. Nos. 6,107,329, 6,277,877, and 6,297,269. The commonly-assigned U.S. Pat. Nos. 6,107,329, 6,277,877, and 6,297,269, the disclosures of which are incorporated herein by reference in their entirety, disclose novel substituted N-(indole-2-carbonyl)-xcex2-alaninamide compounds, including 5-chloro-N-[(1S,2R)-3-[3R,4S]-3,4-dihydroxy-1-pyrrolidinyl]-2-hydroxy-3-oxo-1-(phenylmethyl)propyl]-1H-indole-2-carboxamide, denoted hereinbelow as the compound of Formula (I); certain derivatives thereof; processes for the production thereof; pharmaceutical compositions comprising such compounds or such derivatives; and methods of treating glycogen phosphorylase dependent diseases or conditions by administering such compounds, such pharmaceutical compositions, or such derivatives, to a mammal in need of such treatment.
The present invention relates to improved processes useful in the preparation of the N-(indole-2-carbonyl)-xcex2-alaninamides disclosed in the aforementioned U.S. Pat. Nos. 6,107,329, 6,277,877, and 6,297,269, including 5-chloro-N-[(1S,2R)-3-[3R,4S]-3,4-dihydroxy-1-pyrrolidinyl]-2-hydroxy-3-oxo-1-(phenylmethyl)propyl]-1H-indole-2-carboxamide (I); certain intermediates related thereto; and processes useful in preparing such intermediates.
These improved processes, set forth in detail hereinbelow, provide certain advantages over those processes disclosed in the aforementioned prior art including, for example, reduced costs in preparing final products intended for human administration, minimization of impurities formed in preparing such final products, and a reduced number of synthetic steps required during the preparation of such final products.
The instant invention provides novel processes and intermediates useful in the preparation of certain N-(indole-2-carbonyl)-xcex2-alaninamide compounds, which compounds are glycogen phosphorylase inhibitors useful in the treatment of diseases such as hypercholesterolemia, hyperglycemia, hyperinsulinemia, hyperlipidemia, hypertension, atherosclerosis, diabetes, diabetic cardiomyopathy, infection, tissue ischemia, myocardial ischemia, and in inhibiting tumor growth.
The present invention provides novel processes and intermediates useful in the preparation of certain N-(indole-2-carbonyl)-xcex2-alaninamides. More particularly, the invention provides novel processes for preparing the compound 5-chloro-N-[(1S,2R)-3-[3R,4S]-3,4-dihydroxy-1-pyrrolidinyl]-2-hydroxy-3-oxo-1-(phenylmethyl)propyl]-1H-indole-2-carboxamide (I). The invention further provides intermediates useful in the preparation of the aforementioned compound, and processes for the production of such intermediates.
In one aspect of the invention, there is provided a process for preparing a compound of structural formula (I) 
which process comprises the steps of:
(a) coupling a compound of structural formula (Ia) 
xe2x80x83with 3-pyrroline to provide an amide derivative of structural formula (Ib) 
(b) oxidizing the amide derivative (Ib) formed in Step (a) to provide the compound of structural formula (I).
In the coupling reaction set forth in Step (a), the compound of structural formula (Ia) 
prepared according to the methods disclosed in the aforementioned U.S. Pat. Nos. 6,107,329, 6,277,877, and 6,297,269, is coupled with 3-pyrroline to provide the compound of structural formula (Ib) 
Such coupling reaction may be effected according to standard synthetic methodologies known to one of ordinary skill in the art. For example, such coupling may be effected using an appropriate coupling reagent such as 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), in the presence of 1-hydroxybenzotriazole (HOBT), 2-ethyloxy-1-ethyloxy-carbonyl-1,2-dihydroquinone (EEDQ), CDI/HOBT, propanephosphonic anhydride (PPA), or diethylphosphorylcyanide, and the like, in an aprotic, reaction-inert solvent, such as dichloromethane, acetonitrile, diethylether, tetrahydrofuran, optionally in the presence of a tertiary amine base, such as triethylamine or N,Nxe2x80x2-diisopropylethylamine (Hunig""s Base). Such coupling is typically effected at a temperature range of from about 0xc2x0 C. to about the reflux temperature of the solvent employed. In a preferred embodiment, the coupling reaction is effected at ambient temperature in tetrahydrofuran using EDC, and a catalytic amount of HOBT, in the presence of an organic base selected from triethylamine or Hunig""s Base. The use of Hunig""s Base in such coupling is especially preferred. The 3-pyrroline starting material may be obtained from commercial sources.
The oxidation reaction set forth in Step (b) may be effected according to synthetic methodologies known to one of ordinary skill in the art for converting olefins into cis-diols. Such oxidation may be carried out using ruthenium(III) chloride, with sodium periodate as a co-oxidant, AgO (J. Org. Chem., 61, 4801 (1996)), osmium tetroxide, or a catalyst with N-methylmorpholine N-oxide (NMO) in a reaction-inert, polar organic solvent such as acetonitrile, tetrahydrofuran, alkyl ethers, and the like. In a preferred embodiment, the oxidation of (Ib) to compound (I) is effected using catalytic osmium tetroxide and N-methylmorpholine N-oxide (NMO) in tetrahydrofuran (Rosenberg, et al.; J. Med. Chem., 33, 1962 (1990)).
The product of Step (b) is then preferably isolated according to well-known methodologies known to one of ordinary skill in the art.
In another aspect, the invention provides a process for preparing a compound of structural formula (I) 
which process comprises the steps of:
(a) coupling a compound of structural formula (Ia) 
xe2x80x83with (3aR,6aS)-tetrahydro-2,2-dimethyl-4H-1,3-dioxolo-[4,5-c]pyrrole, p-toluenesulfonate (IVi) 
xe2x80x83to provide an acetonide derivative of structural formula (IIa) 
(b) cleaving the acetonide derivative (IIa) formed in Step (a) to furnish the compound of structural formula (I).
The coupling of compound (Ia) with (IVi) to form the acetonide derivative (IIa) can be effected according to the methods disclosed hereinabove for the preparation of compound (Ib). Preferably, the coupling is performed using EDC and HOBT in the presence of Hunig""s Base. The HOBT may be employed catalytically, i.e., in an amount less than one equivalent. Generally, a range of from about 0.05 to about 0.50 equivalents may be employed in the coupling step, however, it is generally preferred that the HOBT be employed in a catalytic ratio of about 0.15 to about 0.25 molar equivalents of acid (Ia). Although acetonide (IIa) can be employed directly in the subsequent cleavage step, it may occasionally be preferable, for reasons of improved color and purity, to isolate acetonide (IIa) prior to such cleavage. The isolation of the less polar acetonide (IIa) allows a purge of more polar impurities then, following the deprotection step, the more polar substrate (I) is isolated by crystallization, thereby allowing for a purge of less polar impurities that may be present.
The conversion of acetonide (IIa) into compound (I) may be effected according to generally known methods, for example, by treatment of the isolated acetonide (IIa) with a mineral acid, such as hydrochloric or hydrobromic acid, or an organic acid, such as methanesulfonic or p-toluenesulfonic acid, all in the presence of water.
Alternatively, compound (I) may also be conveniently prepared by the production, and in situ cleavage, of acetonide (IIa). The preparation of a solution of acetonide (IIa) in a suitable solvent may be effected as outlined hereinabove. The in situ conversion of acetonide (IIa) into compound (I), described in Example 5 hereinbelow, may also be conveniently effected according to known methods, for example, by treating the solution of acetonide (IIa) with an aqueous mineral acid, such as hydrochloric or hydrobromic acid, or an organic acid, such as methanesulfonic, or p-toluenesulfonic acid, also under aqueous conditions. Compound (I) so produced may then be isolated according to known preparative methods.
In another aspect of the invention, there is provided a process for preparing a compound of structural formula (I) 
which process comprises the steps of:
(a) coupling a compound of structural formula (Ia) 
xe2x80x83with cis-3,4-dihydroxypyrrolidine, p-toluenesulfonate (Vi) 
xe2x80x83to provide an ethanol solvate of structural formula (IIIa) 
(b) desolvating the ethanol solvate (IIIa) formed in Step (a) to furnish the compound of structural formula (I).
The coupling of compound (Ia) to form ethanol solvate (IIIa) may be performed according to those coupling methods previously described hereinabove for the preparation of compound (Ib) and acetonide (IIa). Preferably, the coupling is effected using EDC and HOBT in the presence of a tertiary amine base, such as triethylamine, or Hunig""s Base. The use of Hunig""s Base is especially preferred.
The ethanol solvate (IIIa) may be desolvated to form compound (I) by dissolving (IIIa) in an aprotic solvent, such as ethyl acetate or toluene, distilling the solution to remove residual ethanol, treating the solution with water such that a concentration of water in the range of between about 1% to about 3% water is achieved, and warming the aqueous solution to reflux temperature, at which point crystallization of (I) begins. The addition of seed crystals to the aqueous solution prior to reflux is typically preferred. The reflux period may comprise from a few hours to one or more days, preferably from about eight to about twenty hours. Once crystallization is essentially complete, excess water is removed by azeotropic distillation, preferably at atmospheric pressure, and the slurry is then cooled to between about 5xc2x0 to about 30xc2x0 C., preferably, about room temperature, where the isolation of (I) is performed according to standard methods, such as by filtration.
In yet another aspect, the present invention provides a process for preparing a compound of structural formula (I) 
which process comprises coupling a compound of structural formula (Ia) 
with cis-3,4-dihydroxypyrrolidine free base (V) 
to provide the compound of structural formula (I).
The coupling of compound (Ia) with cis-3,4-dihydroxypyrrolidine free base (V) to form compound (I) may also be performed according to those coupling methods previously described hereinabove for the preparation of compound (Ib), acetonide (IIa), or ethanol solvate (IIIa). The free base of cis-3,4-dihydroxypyrrolidine (V) may be prepared according to the several synthetic methods described in detail hereinbelow including, for example, the process disclosed in Example 18. The compound of structural formula (I) so prepared is then preferably isolated according to standard methodologies that are well known to one of ordinary skill in the art.
Another aspect of the invention provides synthetic methods useful for preparing compound (V), and the acid addition salts thereof, which compound, or which acid addition salts, are intermediates useful in the preparation of compound (I). These exemplary synthetic methods are described in detail hereinbelow in Schemes 1 to 7. The cis-3,4-dihydroxypyrrolidine, p-toluenesulfonate salt (Vi) may be obtained commercially.
In one aspect, the invention provides a process useful in preparing compound (V), or an acid addition salt thereof, which process comprises the steps outlined hereinbelow in Scheme 1. 
As shown in Scheme 1, the 3-pyrroline starting material (Aldrich Chemical Co., Milwaukee, Wis.) is protected with BOC-anhydride in the presence of an organic or Brxc3x6nsted base in an aprotic solvent. The mixture of protected N-BOC-3-pyrroline products (Va) may then be oxidized to the corresponding diol (Vb) according to known methods, for example osmium tetroxide oxidation, the use of catalytic osmium tetroxide with a co-oxidant, the use of ruthenium(III) chloride/sodium periodate (Shing, T. K. M., et al., Angew. Chem. Eur. J., 2, 50 (1996), or Shing, T. K. M., et al., Angew. Chem. Int. Ed. Engl., 33, 2312 (1994)), potassium permanganate, or similar reagents and conditions that will be well-known to one of ordinary skill in the art. The BOC protecting group of (Vb) may be subsequently removed by treatment with a suitable acid, for example, trifluoroacetic acid, methanesulfonic acid, and the like, in the presence of a reaction-inert solvent such as tetrahydrofuran, dichloromethane, or acetonitrile, to form (V).
Preferably, compound (V) is then isolated, either in the form of the free base, or in the form of an acid addition salt thereof, wherein such acid addition salt may be prepared according to known methods. Such acid addition salts, may include, for example, the hydrochloride, hydrobromide, sulfate, hydrogen sulfate, phosphate, hydrogen phosphate, dihydrogen phosphate, acetate, succinate, citrate, methanesulfonate (mesylate), and 4-methylbenzenesulfonate (p-toluenesulfonate) acid addition salts. Such acid addition salts may be prepared readily by reacting compound (V) with an appropriate conjugate acid. When the desired salt is of a monobasic acid (e.g., hydrochloride, hydrobromide, tosylate, acetate, etc.), the hydrogen form of a dibasic acid (e.g., hydrogen sulfate, succinate, etc.), or the dihydrogen form of a tribasic acid (e.g., dihydrogen phosphate, citrate, etc.), at least one molar equivalent, and usually a molar excess, of the acid is employed. However, where such salts as the sulfate, hemisuccinate, phosphate, or hydrogen phosphate are desired, the appropriate and stoichiometric equivalent of the acid will generally be employed. The free base and the acid are normally combined in a co-solvent from which the desired acid addition salt then precipitates, or can be otherwise isolated by concentration of the mother liquor, or by the precipitative effect resulting from the addition of a non-solvent. Especially preferred acid addition salts of compound (V) comprise the p-toluenesulfonate (Vi) and hydrochloride acid addition salts.
An alternative method that may be used to prepare compound (V), or an acid addition salt thereof, comprises the process outlined hereinbelow in Scheme 2. 
As shown in Scheme 2, the dibromo diketone starting material is reduced in the presence of a suitable reducing agent, such as sodium borohydride, in a reaction-inert solvent, such as an ether (tetrahydrofuran or methyl tert-butyl ether), or other suitable solvent(s) to provide a mixture of the syn- and anti-alcohols (VIa) and (VIaxe2x80x2). Alcohols (VIa) and (VIaxe2x80x2) are then cyclized with benzylamine in the presence of a suitable base, such as sodium bicarbonate, to yield diol (VIb). The use of an additive, such as potassium iodide, has been shown to improve the rate of cyclization. See, for example, Larock, Comprehensive Organic Transformations, VCH, New York, 337-339 (1989).
The benzyl protecting group of (VIb) may be subsequently removed by standard methods, such as hydrogenation using a catalyst such as palladium on carbon in a reaction-inert solvent, such as an alcohol or ether, to form compound (V), followed by acid addition salt formation, if desired.
Yet another alternative method that may be employed in the preparation of (V), or an acid addition salt thereof, comprises the process depicted in Scheme 3. 
In Scheme 3, meso-tartaric acid is cyclized with benzylamine to give diol (VIIb). Such cyclization is typically effected in a reaction-inert solvent such as methylene chloride, tetrahydrofuran, or ethyl acetate at temperatures generally above ambient temperature. See, for example, March, Advanced Organic Chemistry, 4th Ed., Wiley Interscience, 420 (1992). It will be appreciated by one of ordinary skill in the art that such amide bond formations from carboxylic acids may be aided by addition of coupling agents such as dicyclohexylcarbodiimide, N,Nxe2x80x2-carbonyidiimidazole, or ethyl-1,2-dihydro-2-ethoxy-1-quinolinecarboxylate (EEDQ). Diol (VIIb) is then reduced to diol (VIb) through the use of known reducing reagents, such as lithium aluminum hydride, diborane, or sodium borohydride, in the presence of boron trifluoride.
The benzyl protecting group of (VIb) may be subsequently removed by standard methods, such as hydrogenation using a catalyst such as palladium on carbon in a suitable solvent, such as an alcohol or ether, to form compound (V), followed by acid addition salt formation, if desired.
Yet another method useful in the preparation of compound (V), or an acid addition salt thereof, comprises the steps shown in Scheme 4. 
In Scheme 4, the butane-tetraol starting material is converted to diactetate (VIIa) under standard conditions, such as treatment with hydrobromic acid and acetic acid, or by those methods described in Talekar, D. G., et al., Indian J. Chem., Sect. B, 25B (2), 145-51 (1986), or Lee, E., et al., J. Chem. Soc., Perkin Trans. 1, 23, 3395-3396 (1999). Diacetate (VIIIa) is then cyclized with benzylamine in the presence of a suitable base, such as sodium bicarbonate, to give (VIb). As disclosed hereinabove, the use of an additive, such as potassium iodide, to assist cyclization may be employed if desired, or appropriate.
The benzyl protecting group of (VIb) may be subsequently removed by standard methods, such as hydrogenation using a catalyst such as palladium on carbon in a suitable solvent, such as an alcohol or ether, to form compound (V), followed by acid addition salt formation, if desired.
Yet another method useful in the preparation of (V), or an acid addition salt thereof, comprises the process shown in Scheme 5. 
In Scheme 5, (E)-1,4-dichloro-2-butene is di-hydroxylated to furnish diol (IXa) employing conditions known to one of ordinary skill in the art, for example, hydrogen peroxide and formic acid, or m-chloroperoxybenzoic acid and water. Diol (IXa) is then cyclized with benzylamine in the presence of a suitable base, such as sodium bicarbonate, to give diol (VIb). As disclosed hereinabove, the use of an additive, such as potassium iodide, to assist cyclization may be employed if desired, or appropriate.
The benzyl protecting group of (VIb) may be subsequently removed by standard methods, such as hydrogenation using a catalyst such as palladium on carbon in a reaction-inert solvent, such as an alcohol or ether, to form compound (V), followed by acid addition salt formation, if desired.
Yet another method useful in the preparation of (V), or an acid addition salt thereof, comprises the process depicted in Scheme 6. 
In Scheme 6, (Z)-1,4-dichloro-2-butene is di-hydroxylated to furnish diol (IXa) according to synthetic methods known to one of ordinary skill in the art. For example, such oxidation may be effected employing a mixture of sodium periodate and a ruthenium salt in a reaction-inert, aprotic solvent such as acetontrile, or a halogenated hydrocarbon solvent such as chloroform, methylene chloride, or carbon tetrachloride. Where appropriate or desired, solvent mixtures comprising reaction-inert, aprotic solvents, for example, acetonitrile and ethyl acetate, may also be utilized. In a preferred embodiment, the oxidation reaction is effected utilizing ruthenium(III) chloride hydrate and sodium periodate in a cooled acetonitrile/ethyl acetate solvent mixture. Diol (IXa) is then cyclized using benzylamine in the presence of a suitable base, such as sodium bicarbonate, to furnish compound diol (VIb). As disclosed hereinabove, the use of an additive, such as potassium iodide, to assist in cyclization may be employed if desired, and/or appropriate.
The benzyl protecting group of (VIb) may be subsequently removed by standard methods, such as hydrogenation using a catalyst such as palladium on carbon in a suitable solvent, such as an alcohol or ether, to form compound (V), followed by acid addition salt formation, if desired.
Yet another method of preparing compound (V), or an acid addition salt thereof, comprises the process shown in Scheme 7. 
As shown generally in Scheme 7, the aminodiol starting material is protected with BOC-anhydride in the presence of an organic or Brxc3x6nsted base in an aprotic solvent. The BOC protected diol (XIa) is then oxidized to dialdehyde (XIb) by methods generally known to those skilled in the art. For example, diol (XIa) may be oxidized using a strong oxidant such as potassium permanganate, ruthenium tetroxide, manganese dioxide, or Jones"" reagent (chromic acid and sulfuric acid in water). Alternatively, oxidation of (XIa) to (XIb) may be effected by catalytic dehydrogenation using reagents such as copper chromite, Raney nickel, palladium acetate, copper oxide, and the like. For additional examples see, for example, March, Advanced Organic Chemistry, 2nd edition, Wiley-Interscience, 1992. The dialdehyde (XIb) may then be cyclized to BOC-protected diol (Vb) via pinacol coupling. Known methods of effecting such coupling may comprise direct electron transfer using active metals such as sodium, magnesium, or aluminum, or through the use of titanium trichloride. The BOC-group of (Vb) can then be removed by treatment with a suitable acid as described hereinabove.
Preferably, compound (V) is then isolated, either in the form of the free base, or in the form of an acid addition salt thereof, wherein such acid addition salt may be prepared as described hereinabove.
Another aspect of the instant invention provides synthetic methods useful for preparing compound (IV) hereinbelow, and the acid addition salts thereof, which compound and acid addition salts, are also intermediates useful in the preparation of compound (I). Such exemplary synthetic methods are depicted in detail hereinbelow in Schemes 8 to 10.
In one aspect, compound (IV), or an acid addition salt thereof, may be prepared according to the process shown in Scheme 8. 
As shown in Scheme 8, ribose is protected by forming the acetonide derivative (XIIa) thereof. Such acetonide formation can be effected in a variety of ways, for example, according to those methods described in Greene, T. W., et al., Protective Groups in Organic Synthesis, 2nd Edition, Wiley-Interscience, (1991). As an example, the formation of protected diol (XIIa) may be performed using acetone in the presence of iodine. The oxidation of (XIIa) to (XIIb) may be effected using reagents including sodium periodate in methanol. The reduction of (XIIb) may be performed according to known methods, for example, through the use of lithium aluminum hydride or sodium borohydride in the presence of acid, such as acetic acid. Amine (IVc) is prepared by treating (XIIb) with benzylamine in methylene chloride or similar reaction-inert solvents.
The benzyl protecting group of (IVc) can be subsequently removed according to standard methods, such as hydrogenation, using a catalyst such as palladium on carbon in a suitable solvent, such as an alcohol or ether, to form compound (IV).
Preferably, compound (IV) is then isolated, either in the form of the free base, or in the form of an acid addition salt thereof, wherein such acid salt may be prepared as described hereinabove. Especially preferred acid addition salts of compound (IV) are the p-toluenesulfonate (IVi) and hydrochloride acid addition salts.
Yet another method for the preparation of compound (IV), or an acid addition salt thereof, comprises the process illustrated in Scheme 9. 
wherein Piv represents the pivaloyl moiety, i.e., (CH3)3C(O)xe2x80x94.
As shown in Scheme 9, meso-erythritrol is protected using standard methodologies to form the di-pivaloyl derivative (XIIIa). Such protection is preferably effected using pivaloyl chloride in the presence of a strong organic base, such as pyridine. The resulting diol (XIIIa) may be protected by formation of the acetonide (XIIIb) by treatment of (XIIIa) with tosic acid in acetone or by treatment with 2,2-dimethoxypropane (DMP). The Piv- groups of (XIIIb) may be subsequently removed according to standard methods, for example those methods disclosed in Greene, T. W., et al., Protective Groups in Organic Synthesis, 2nd Edition, Wiley-Interscience, (1991), to form deprotected derivative (XIIIc). As an example, the deprotection of (XIIIb) may be effected using a strong inorganic base, such as sodium or potassium hydroxide, in an aqueous solvent, such as an alcohol. Mesylate activation of the diol (XIIIc), in a suitable non-reactive solvent in the presence of a base such as triethylamine, gives compound (XIIId). Cyclization of (XIIId) with benzylamine in the presence of a base, such as an organic amine, affords (IVc). The benzyl protecting group of (IVc) can be subsequently removed according to standard methods, such as hydrogenation, using a catalyst such as palladium on carbon in a suitable solvent, such as an alcohol or ether, to form compound (IV).
Preferably, compound (IV) is then isolated, either in the form of the free base, or in the form of an acid addition salt thereof, wherein such acid salt may be prepared as described hereinabove.
In another aspect, the invention provides a generally preferred process for the preparation of compound (IV), or the preferred p-toluenesulfonate acid addition salt (IVi) thereof, which process is depicted hereinbelow in Scheme 10. 
The oxidation of N-benzylmaleimide to diol (VIIb) may be performed according to synthetic methods known to one of ordinary skill in the art. For example, such oxidation may be effected employing a mixture of sodium periodate and a ruthenium salt in a reaction-inert, aprotic solvent such as acetonitrile, or a halogenated hydrocarbon solvent such as chloroform, methylene chloride, or carbon tetrachloride. Where appropriate or desired, solvent mixtures comprising reaction-inert, aprotic solvents, for example, acetonitrile and ethyl acetate, may also be utilized. In a preferred embodiment, the oxidation reaction is effected utilizing ruthenium(III) chloride hydrate and sodium periodate in a acetonitrile/ethyl acetate solvent mixture at below ambient temperature.
The formation of acetonide (IVb) may be effected according to synthetic methodologies known to one of ordinary skill in the art. For example, such protection may be performed by condensing diol (VIIb) with acetone, 2,2-dimethoxypropane, or a mixture of both, in the presence of an acid catalyst, such as sulfuric, p-toluenesulfonic, or methanesulfonic acid. In a preferred embodiment, the protection reaction is effected by condensing diol (VIIa) in 2,2-dimethoxypropane with a catalytic amount of methanesulfonic acid.
The reduction of acetonide (IVb) to (IVc) may be effected according to synthetic methodologies known to one of ordinary skill in the art. For example, such reduction may be performed using a boron or aluminum hydride complex including, for example, BH3THF, BH3etherate, or Red-Al(copyright) (sodium bis(2-methoxyethoxy)aluminum hydride; Aldrich Chemical Co., Milwaukee, Wis.), in an aprotic, reaction-inert solvent, such as toluene or diethylether. In a preferred embodiment, the reduction of protected acetonide (IVb) to (IVc) is effected using Red-Al(copyright)in toluene.
The deprotection of (IVc) may be effected according to synthetic methodologies known to one of ordinary skill in the art. For example, such using palladium salts, or complexes, such as Pd(OH)2, or Pd/C in polar, protic solvents, such as methanol or ethanol, in a non-protic solvent, such as tetrahydrofuran, or in a mixture of such solvents. Alternatively, such deprotection may be effected under hydrogenation-transfer conditions, i.e., Pd/C with cyclohexene. In a preferred embodiment, the deprotection reaction is effected using Pd(OH)2/C in methanol.
The deprotected product (IV), is then preferably isolated, in the form of the preferred p-toluenesulfonate acid addition salt (IVi) thereof, which may be either prepared as described hereinabove, or obtained commercially.
The present invention is illustrated by the following Examples. It is to be understood, however, that the Examples hereinbelow are provided solely for the purpose of illustration, not limitation.
The cis-3,4-dihydroxypyrrolidine, p-toluenesulfonate salt (Vi) was purchased from Aldrich Chemical Co., Fine Chemicals Division, Milwaukee, Wis.